F-Twins Tech – F650/700/800 - Renewing Brake Fluid

[drneo66]

The articles, posts and comments in this tech section are posted by individual members and reflect their personal thoughts and experiences with repairing, maintaining, and generally working on motorcycles. This information may require specific knowledge and skills, may or may not be correct or current to model.

The authors of information found here and the BMW MOA take no responsibility for ensuring the accuracy of any information (including procedures, techniques, parts numbers, torque values, tool usage, etc.), or further for any damage of any kind or injuries incurred or caused by anyone following the instructions or information found here.

It is the duty of the individual to either assume the liability himself for responsibly using the information found here, or to take the bike or accessory to a Dealer or other qualified professional service.

Please ensure you dispose of your used chemicals, oils and fuels in an environmentally responsible manner. Most Auto Parts stores and service stations will accept used oil and lubricants, tires and batteries, please check for your local availability. Here's a link where you can look up a place to dispose of your used fluids (oil, coolant, brake fluid, etc.) - http://earth911.com/

This article, text and photos are Copyright of the individual authors and the BMW MOA, any copying or redistributing is permitted only by prior written authorization.

PLEASE PRINT AND READ ALL THE INSTRUCTIONS BEFORE BEGINNING!

Final note: PLEASE ONLY DO THIS JOB IF YOU ARE COMPETENT WITH TOOLS - Brake failure is no fun! When in doubt, take your motorcycle to a reputable dealer.

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Renewing the brake fluid in the front and rear brakes on your BMW twin-cylinder F650, F700 and F800.


The F-Twin manual calls for the brake fluid to be replaced every two years, and that's for good reason. Because brake fluid is hygroscopic, it naturally absorbs moisture from the surrounding air, which causes the boiling point of the fluid to decrease. A lowered boiling point could cause your brakes to fail (often at an inopportune time) because the liquid (which is not compressible) can turn to vapor (which is compressible) at higher temperatures. Brake fluid will absorb moisture whether you're riding 50,000 miles per year, or 5 miles.

DOT 4 brake fluid, which is recommended by BMW for our F-Twins, has a minimum boiling temperature of 446 degrees Fahrenheit when it's fresh out of the can. After absorbing just a small amount of water, that boiling temperature number can almost be cut in half. From what I was able to find, most DOT brake fluid will absorb about 3-4% moisture by volume after just two years. After the brake fluid absorbs about 8% of of it's total volume, the boiling point is almost no better than plain water.

The second reason that we want to replace the fluid in the brake system is because it also contains corrosion inhibitors. These inhibitors can prevent problems in our delicate ABS systems (if your bike is equipped). So, at the end of the day, a little $4 bottle of brake fluid can save you time, money, and possibly your life.



Note 1: The specific bike shown is a 2013 F800GS
Note 2: The 650 version of the F-Twins will only have one brake caliper and disc on the front wheel
Note 3: The tools and materials used are by personal choice and are not due to any affiliation with any brand


Tools Required:
- 11mm wrench
- Clear tubing that fits the bleeder nipple and small container or a vacuum bleeder (we will be using a Mityvac for this post)
- Torque wrench and 11mm socket
- Optional - T25 star (Torx) wrench or bit and ratchet

Materials Required:
- An unopened bottle of Dot 4 brake fluid
- Suitable bottle to hold used brake fluid for proper disposal


WARNING: Brake fluid attacks paint. Depending on the type of paint - the attack can be very fast, or relatively slow - but your goal in doing this job is to avoid getting brake fluid on any paint. IF you do get fluid on painted parts - a rinse with soapy water is a very good thing to do - as soon as you can. If you delay too long you'll be washing the paint off along with the fluid.

[drneo66]

Let's start with the rear brake. The rear brake reservoir is indicated by a green arrow.


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[drneo66]

I like to carefully unscrew the rear reservoir from the frame (using your T25 star bit) to make it easier to unscrew the cap and refill the master as needed. Make sure you put your least-favorite t-shirt around the reservoir as not to harm your paint. The cap simply screws off. There will be a plastic ring and a rubber stopper that will also need to be removed. Make sure you put these in a safe place as not to get brake fluid on any painted surfaces

I like to try to remove as much of the old fluid as possible from the reservoir before adding fresh new fluid. I use the MityVac to suck up this fluid, but you could also use a clean paper towel to carefully remove it. Just be careful as not to let any air into the system.

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[drneo66]

Next, we will remove the protective rubber cap from the rear brake. Take a moment to clean the area around the bleeding nipple, as we don't want to introduce any contaminants into the brake system.

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[drneo66]

We want to retract as much of the brake pistons back into the caliper as possible, as this will reduce the amount of brake fluid that's left in the caliper body. Most of the time you just need to use your hand to gently push the caliper against the brake disc. Alternatively, you can remove the caliper and use an appropriate tool to push the pistons back. The pistons live under the rounded portion of the caliper body, so pushing on the white "B" (on the caliper) towards the brake disc, should retract the piston into the caliper.

After that, we will hook up our bleeding equipment.

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[drneo66]

Start pumping the Mityvac to pull negative pressure, and then open the bleed nipple about an 1/8th of a turn, using your 11mm wrench. If you open the bleed nipple too far, you have the possibility to suck some air into the system, so again, don't open it too far. You should see some fluid begin to flow in the clear Mityvac tubing. Keep pumping the Mityvac until you have nearly removed all the the brake fluid in the rear reservoir. Again, make sure not to suck any air into the brake system. Always keep a vacuum on the system until you close the bleed nipple, if we don't, we have the possibility of adding air into the system. You will probably go through a bit of brake fluid doing this procedure, as the fluid has to travel from the reservoir, through the ABS pump (if equipped) through all the lines, and finally exit at the brake caliper. Always make sure you have a bit of fluid in the reservoir to prevent air entering the system (I can't type this enough).

If you don't have a vacuum bleeder, it will be a bit more work, but you can still flush the brakes. Having two people also helps. First, hook up the appropriately-sized tubing to the bleed nipple and submerge the other end in a bit of brake fluid (this reduces the chances of sucking air back into the system). Then, gently push down the brake pedal until you feel resistance. This will put pressure into the brake system. Open the bleed nipple about an 1/8th of a turn using your 11mm wrench. Brake fluid should start to flow and the pedal will travel further down its stroke. Try not to go all the way down and bottom out the master cylinder as this could introduce problems with the cylinder seal. Before releasing the brake pedal, close the bleeder nipple. Repeat this process - pressure, open, plunge brake pedal, close, pressure, etc. until you see fresh brake fluid exiting at the bleeder nipple.


Fresh, clean brake fluid is a very light honey color. The brake fluid that was flushed out of this bike was very dark, signifying how badly it was due to be changed.

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[drneo66]

Continue to flush the system until you see fresh fluid emerge.

Note: if you have an ABS equipped bike, and the appropriate diagnostic tool (GS911 or Motoscan), use that tool to do an ABS bleed test. This will activate the ABS system, mixing in any old remaining fluid or air into the newer brake fluid. You then have to flush the system one more time to pull that fluid out. An alternative is to button everything back up, and go find an area that you can SAFELY activate the ABS system. This is not as good (and could be dangerous) as the appropriate electronic gadget, but in theory, it would mix a bit of the old and new brake fluid together, allowing you to proceed back to your garage and flush the system again.

When you're satisfied that you have fresh fluid in the whole system, close and tighten the bleed nipple (Torque is: 14 Newton Meters, 10.3 Foot-Pounds or 124 Inch-Pounds) and wipe off any spilled brake fluid. Make sure to put the rubber cap back on to prevent any dirt from entering that area. Top off the rear brake reservoir so that it's about 80% full then replace the rubber stopper, plastic topper piece and screw top. Then using the rear brake pedal, pump the brake pistons until they are pressing against the brake disc. Make sure that the brake fluid is still at an appropriate level, and then screw the reservoir back into the frame (if you removed it).

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[drneo66]

Now, let's head to the front brake. The F700's and F800's have two brake calipers up front. On the F700GS and F800GS, there is a longer brake line that goes down the fork, to the clutch-side brake caliper, then a second smaller brake line goes up and over the front wheel, to the throttle-side caliper. The other F800 variants have one brake line from the master cylinder that splits to each of the brake calipers near the head stock. Our goal is to flush each line and each caliper.

I found it easiest to put the bike on the kickstand, then turn the handlebars fully to the right. This helps level the front master cylinder. Apparently, brake fluid theft may be a concern in some areas of the world, so BMW designed a locking cap. This cap has two tabs at the 3 and 6 O'clock positions that must be pushed in before we can spin the cap off. It's somewhat similar to a pill bottle? Some people can squeeze those areas with their fingers, and their caps have enough give that they are able to unlock the cap. I found that using two zip ties, pressed in with my thumb and forefinger does the trick.

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[drneo66]

Next, we will set the cap aside and gently remove the plastic spacer and inner rubber gasket/diaphragm. Make sure to put these someplace clean, as we don't want to introduce any contaminates into the system.

Here you can see one of the tabs that we are trying to push in that unlocks the cap.

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[drneo66]

Let's remove most of the fluid using a clean paper towel, turkey baster, or your vacuum pump. Just like the rear master cylinder, we don't want to remove all of the fluid, as that would introduce air into the system.

Again, we will push the brake pads as far "in" as we can at the caliper. Then we will fill the front master cylinder back up to near the top of the reservoir with our freshly-opened DOT 4 brake fluid.

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[drneo66]

Because of the odd route that the brake lines take on the GS's, we want to start with the caliper that is furthest from the master cylinder. On the GS's, this is the throttle side. On the ST/GT, flip a Loonie to determine which side you want to start on.

Get your vacuum bleeder ready, plus your 11 mm wrench, and start pumping the Mityvac to pull negative pressure, then open the bleed nipple about an 1/8th of a turn. You should see some fluid begin to flow in the clear Mityvac tubing. Keep pumping the Mityvac until you have nearly removed all the the brake fluid in the front reservoir. Again, make sure not to suck any air into the brake system. Keep adding more fluid to the reservoir and vacuuming fresh fluid at that caliper until the brake fluid runs very clear. You may be surprised by the amount of fluid that you need, since the fluid has to go into the ABS system and through of those lines before ending up at the caliper.

Again, if you're not using the vacuum bleeder use the same sequence as mentioned in the rear brake breeding section above - pressure, open, plunge brake handle, close, pressure, etc. until you see fresh brake fluid exiting at the bleeder nipple. As with the rear brake, we don't want the lever to travel more than "normal operating range," and a trick to prevent that, is to tie a spacer to the handlebar (a piece of wood works nicely). The spacer will prevent the front brake handle from going too far.

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[drneo66]

We can now repeat the same process at the other caliper.


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[drneo66]

Note: if you have an ABS equipped bike, and the appropriate diagnostic tool (GS911 or Motoscan), use that tool to do an ABS bleed test. This will activate the ABS system, mixing in any old remaining fluid or air into the newer brake fluid. You then have to flush the system one more time to pull that fluid out. An alternative, is to button everything back up, and go find an area that you can SAFELY activate the ABS system. This is not as good (and could be dangerous) as the appropriate electronic gadget, but in theory, it would mix a bit of the old and new brake fluid together, allowing you to proceed back to your garage and flush the system again.

When you're satisfied that you have fresh fluid in the whole system, close and tighten the bleed nipple (Torque is: 14 Newton Meters, 10.3 Foot-Pounds or 124 Inch-Pounds) and wipe off any spilled brake fluid. Make sure to put the rubber cap back on to prevent any dirt from entering that area. Top off the front brake reservoir so that it's about 80% full and using the front brake lever, pump the brake pistons until they are pressing against the brake disc. Make sure that the brake fluid is still at an appropriate level, and then replace the rubber diaphragm, plastic topper piece and screw top.

Take moment to double check for any leaks. With the bike standing upright, double check that you have full braking at both the front and rear wheels. Put on your gear and go for a short test ride, when finished, again look for any leaks or problems.

Happy riding (and stopping)!

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